The general method for producing (meth)acrylic acid includes a step (A) of reacting propane, propylene, or isobutylene and/or (meth)acrolein, with molecular oxygen or a molecular oxygen-containing gas by gas-phase catalytic oxidation method, adding a reaction gas containing the resultant (meth)acrylic acid in water to prepare an aqueous solution thereof, and then removing low-boiling components such as water and acetic acid from the aqueous solution to obtain crude (meth)acrylic acid; and a step (B) of purifying the resultant crude (meth)acrylic acid to obtain a (meth)acrylic acid product. Further, the (meth)acrylic acid produced by the above method is reacted with alcohol in a step (C) to produce (meth)acrylic esters.
In general, the crude (meth)acrylic acid produced in the above step (A) is sufficiently usable as raw (meth)acrylic acid for production of the (meth)acrylic esters. For this reason, a method in which a part of the crude (meth)acrylic acid produced in the step (A) is fed to the step (B) for producing the (meth)acrylic acid product therefrom, whereas a remainder of the crude (meth)acrylic acid is fed to the step (C) for producing the (meth)acrylic esters therefrom, has been preferably conducted from the standpoints of good production efficiency of the respective products as well as economical merits such as low installation costs.
As described above, in the case where the crude (meth)acrylic acid obtained in the plant used in the step (A) is fed to the plants used in the steps (B) and (C) disposed in parallel with each other, when any one of the plants used in the steps (B) and (C) is stopped owing to failure thereof, the crude (meth)acrylic acid to be fed to the stopped plant is temporarily stored in a tank, thereby enabling the other steps to be operated continuously.
As the conventional method for consuming the crude (meth)acrylic acid stored in the tank, there is known such a method in which the amount of the crude (meth)acrylic acid fed from the plant used in the step (A) to the plants used in the steps (B) and (C) is reduced by lowering an operation load of the plant used in the step (A), and the crude (meth)acrylic acid stored in the tank is fed to the plants used in the steps (B) and (C) in such an amount corresponding to the reduction in amount of the crude (meth)acrylic acid fed from the plant used in the step (A), thereby controlling the amount of the crude (meth)acrylic acid stored in the tank. This is because the operation capacity of the plant used in the step (A) has been conventionally designed so as to be identical to or slightly larger than a total operation capacity of the plants used in the steps (B) and (C) in the consideration of future expansion of amount of products produced. More specifically, since the amount of the crude (meth)acrylic acid produced in the step (A) is identical to or larger than the amount of the crude (meth)acrylic acid consumed in the steps (B) and (C), it has been conventionally required to reduce the operational load of the plant used in the step (A) in order to treat the surplus crude (meth)acrylic acid stored in the tank.
However, if the operational load of the plant used in the step (A) is varied, for example, if the operational load of a distillation column used in the step (A) for removal of low-boiling components is varied, the (meth)acrylic acid tends to be polymerized in the distillation column, resulting in troubles such as clogging due to resultant polymers thereof. In particular, in the case where an aqueous acrylic acid solution is distilled in an azeotropic separation column in the presence of an azeotropic solvent, the distillation procedure tends to be adversely affected by the variation in operational load of the column.
As the method of stably operating the distillation column for a long period of time, while preventing occurrence of clogging due to polymerization therein even if the operational load of the distillation column is varied, there is known such a method in which upon reduced operation where the amount of (meth)acrylic acid produced is reduced by α % as compared to that under ordinary operation conditions, the flow amount of liquid/gas within the distillation column is controlled to (100−α/2)% or more relative to a flow amount under the ordinary operation conditions (for example, Japanese Patent Application Laid-open No. 2003-183219). However, in the above method, since the operational load is also varied, occurrence of defects due to the varied operational load is inevitable.
Accordingly, hitherto, it has been demanded to provide a method capable of treating the crude (meth)acrylic acid temporarily stored in the tank when the step (B) or (C) is stopped without any substantial change in operational load of the step (A).